Liquid-crystalline mixtures, in particular ferroelectric liquid-crystalline mixtures

Abstract

The novel liquid-crystalline mixtures (in the case of ferroelectric behavior they additionally contain an optically active compound as dope) are based on at least two mixture components of the general formula (I) and at least one carboxylate of the general formula (II), (III) or (IV). ##STR1## The mixtures have favorable properties for use in electrooptical display elements, such as high contrast, low melting point and short switching times.

We claim: 
     
       1. A liquid-crystalline mixture containing, as component A, at least two 5-alkoxy-2-(alkoxyphenyl)pyrimidines of the general formula (I) ##STR54## in which the alkyl radicals are straight-chain alkyl radicals in which n is an integer from 6 to 14 and x is an integer from 2 to 14, wherein the liquid-crystal mixture furthermore contains at least one component c of the general formula (V), (VI), (VII), (VIII) or the racemic mixture of one or more carboxylates of the general formula (IX) as a mixture component: ##STR55## where k may be an integer from 6 to 14, and   l may be an integer from 2 to 14, ##STR56##  where m may be an integer from 5 to 14, and   l may be an integer from 2 to 14, ##STR57##  where p may be an integer from 7 to 14, and   r may be an integer from 4 to 14, ##STR58##  where s may be an integer from 6 to 14, and   t may be an integer from 6 to 14, ##STR59##  where R 2  is straight-chain or branched (C 1  -C 12 )alkyl or alkenyl, it being possible for one or two non-adjacent CH 2  groups to be replaced by O and/or S atoms,   y is F, Cl, Br, CN or CF 3  and   R 1  is branched (C 3  -C 9 )alkyl, benzyl or phenyl.   
     
     
       2. A liquid-crystalline mixture as claimed in claim 1, which contains, as component C, one or more 4-(5-alkylpyrimidin-2-yl)phenyl carboxylates of the general formula (V) ##STR60## where k may be an integer from 6 to 14, and l may be an integer from 4 to 14.   
     
     
       3. A liquid-crystalline mixture as claimed in claim 1, which contains, as component C, one or more 4-(5-alkoxypyrimidin-2-yl)phenyl carboxylates of the general structure (VI) ##STR61## where m may be an integer from 6 to 14, and l may be an integer from 4 to 14.   
     
     
       4. A liquid-crystalline mixture as claimed in claim 1, which contains, as component C, one or more benzoates of the general structure (VII) ##STR62## where p may be an integer from 7 to 14, and r may be an integer from 4 to 14.   
     
     
       5. A liquid-crystalline mixture as claimed in claim 1, which contains, as component C, one or more benzoates of the general structure (VIII) ##STR63## where s may be an integer from 6 to 14, and t may be an integer from 6 to 14.   
     
     
       6. A liquid-crystalline mixture as claimed in claim 1, which contains, as component C, the racemic mixture of one or more of the following carboxylates of the general structure (IX) ##STR64## where R 2  is straight-chain or branched (C 1  -C 12 )alkyl or alkenyl, it being possible for one or two nonadjacent CH 2  groups to be replaced by O and/or S atoms, y is F or Cl and   R 1  is branched (C 3  -C 9 )alkyl, benzyl or phenyl.   
     
     
       7. A liquid-crystalline mixture as claimed in claim 1, which contains, as component C, the racemic mixture of one or more of the following carboxylates of the general structure (IXa) ##STR65## where R 2  is straight-chain or branched (C 1  -C 12 )alkyl or alkenyl, it being possible for one or two nonadjacent CH 2  groups to be replaced by O and/or S atoms, and y is F or Cl.   
     
     
       8. A liquid-crystalline mixture as claimed in claim 1, which contains, as component C, the racemate of the following ester (IXb) ##STR66## 
     
     
       9. A liquid-crystalline mixture as claimed in claim 1, which contains, as component C, the racemate of the following ester (IXc) ##STR67## 
     
     
       10. A liquid-crystalline mixture as claimed in any one of claims 6 to 9, which contains, as component C, 2 to 20 mol-% of one or more of the racemic α-substituted carboxylates. 
     
     
       11. A liquid-crystalline mixture as claimed in claim 1, which contains, as component C, 2 to 40 mol-% of one or more of the mixture components of the general formula (V) and/or (VI) and/or (VII) and/or (VIII). 
     
     
       12. A liquid-crystalline mixture as claimed in claim 1, which further contains one or more cyclohexanecarboxylates of the general formula (II) ##STR68## in which R 1  is an alkyl radical having 10 to 16 carbon atoms or an alkoxy radical having 8 to 14 carbon atoms, and R 2  is an alkyl radical having 2 to 9 carbon atoms. 
     
     
       13. A liquid-crystalline mixture as claimed in claim 1, which further contains one or more alkenyloxyphenylpyrimidine derivatives of the general formula (III) ##STR69## in which R 3  is an alkyl chain having 7 to 16 carbon atoms or an alkoxy chain having 6 to 14 carbon atoms, and y is an integer from 4 to 14. 
     
     
       14. A liquid-crystalline mixture as claimed in claim 1, which further contains one or more alkylpyrimidinealkoxyphenyl derivatives of the general formula (IV) ##STR70## in which m and p, independently of one another, are integers from 6 to 14. 
     
     
       15. A liquid-crystalline mixture as claimed in claim 1, which further contains as component B (for ferroelectric liquid-crystal mixtures), at least one optically active compound from the group a) optically active esters made from α-chlorocarboxylic acids and mesogenic phenols,   b) optically active esters of N-acylpropline,   c) optically active esters of 1,3-dioxolane-4-carboxylic acids,   d) optically active esters of oxirane-2-carboxylic acids.